Stabilized organic compositions



Patented Sept. 8, 1953 De Pree, Royal Oak;v Micha, as'signorsi to Ethyl- Corporation, New York, Y'.',.a corporation of Delaware No Drawing. Original application; December 9; 1950, Serial No-. 200, 116. Divided anditliis an plication- July 27; I953, Sfial NO." 3735102 4 Claims. 1.

This invention relates to the stabilization. of elastomers. More particularly, our invention ne lates to-inhibition of attack by oxygen; and the prolongationof the'usefuhlife of elastomer: com-' positions. co-pending application, Serial No. 200,116, filed December 9, 1950.

All elastomeric materials are more orxlesssusceptible todeterioraticn by oxygen or' ozone. By such materials We refer to both the naturally oc-' curring rubbers and the various synthetic rubber.v on rubber-like elastomers. The degradation of such materials occurs both in the uncured or. in-"- 'termediate stages as well as in the finished, compounded or fabricated stage. Naturally occurring rubbers after coagulation of the latex and-synthetic elastomers after polymerizationand coagulation are particularly susceptible to the action of oxygen, ozone and light. Before useful articles can be fabricated from such elastomersvarious compounding, milling, vulcanization, curing, calendering, molding, extrusion or other'processes or combinations thereof must be performed; di1'r-- ing any of which operations such exposure can occur, and some means of protection is required to' permit successful manufacture of" the desired stock or article. Furthermore, during storage" and use such exposure is encountered" with deleterious effects unless suitable protective" measures are taken.

This exposure can result in the destructionto a. greater or less extent of certain useful physical properties and in the introduction of certain properties which render articles manufactured from such elastomers of limited utility. By adsorption of oxygen or ozone such elastomers deteriorate prematurely, lose tensile strength and flexibility and become discolored, embrittled and surface cracking may occur. While certain ma terials have been proposed forthe protection-of suchelastomers from the deleterious-action:of oxygen, most of such protective substances; as for example fi-naphthol, possess the serious disadvantage, particularly with respecttolight colored stocks, that the decomposition. products" of the protectant are themselves colored-and hence interfere with the color fastness of the stocks being protected.

It" is a primary object of our invention to provide a class of compounds which possess the ability of inhibiting deterioration of elastomeric or plasticsubstances in the. presenc'e ofoxygen; A further object of our invention is-to=retard the deterioration of such substanceswhichmormally are susceptible to'attack by oxygen or' ozone-, and

This application is a divisionof our which: thereby. lose the utility in the service for which they were" manufactured, compounded or otherwise prepared. A .more particular obj ect is to r'enderr elastomer: stocks and elastomer compositionsi stable on prolonged storage or during manufacture. or'use' inthe presence of oxygen. stillother objects: will appear hereinafter.

.Theabove objects: can be accomplished by" pra-cticirigfouri invention which comprises addingv to organic materials'a"small' proportion 0f asub-' stance derived? from the class of hydroxy and amino-substituted plienyl-ureas' and +thioureas. Our: invention resides-not in the determination certain: elastomeridmaterials can be" treated to preventioxida'tivedeterioration, .butratherin pro viding: a class: of compounds: which has broad utilityin providingrsu'ch e protection.

In I general the: compounds: of'our' invention can be defined asith'ose which contain the grouping R. R}Nfi.C'-N it; wherein RIi-i's-allyl} aryl, or R5, R2 is hydroxy pheiiyl or aminophenyr Rb is hydrogen, alkyl' or ary1 and X is the oxygen or sulfuratom. Whenever the further description of our invention hereinafter we-refr'tc" the term" alkyl, it is to understood that weinclude straight chain; branched chain'- and' cyclic saturated hydrocarbon radicals; Exaiifples' of such alkyl'radicals inemdemethyr, ethyl? prom-1, n-octadecyl, iso- '1", see-but yr, Z-IhethYll'iBXYl. cyclohex I mjetliylcyclol-iexyl}fl cyclohexylethyl, etc.

T6 urther'i-llustrate' tl-ie n'ature of' these protective s'ulistances tliegeneralized formula is presented to depict the substituted ureas andthioureas of our mventi'on wherein R1 represents alkyLor ary1 radicals, X. stands for the oxygen or sulphuratom'; R's; and R i'represent hydrogen-or organic radicals'further 'dfinedliereinafter; and" 7 A .refers'to" the ac'tivatifig"gro1.ips described" here"; inafteri L ber's" inserted in the plienyl 'radicalmare" for the purpose of naming specific embodiments-of en? invention hereinafter. We have found that such Iii this generalized" formula the" num-- droxyphenyl, o

4- wherein the symbols have the same meaning as described hereinbefore. The reactants are mixed, in an appropriate solvent, at a temperature of about 50 C. and in a few hours the reaction product crystallizes and is recovered. By this method for example we have prepared the following compounds of our invention: N-(n-propyl) -N'- (phydroxyphenyl) urea, N phenyl-N'-(p-hydroxygroup substituted with one ofthe components A.

In general the phenyl substituents, A, which we refer to as activating groups, comprise amino and hydroxy radicals and hydrocarbon: derivatives thereof. Thus, we can illustrate the group A by amino, N methylamino, N,N dimethylamino,.

N,N-diethylamino, N,N-methylethylamino, N,N- ethylbutylamino, N,N-diisopropylamino, N-cyclohexylamino, N,N-eyclohexylmethylamino, hydroxy, 'etc. Thus, examples of the hydroxyphenyl and aminophenyl groups of our invention which impart the distinctive antioxidant activity to our stabilizing compounds include p-hyhydroxyphenyl, m hydroxyphenyl, 3 methyl 4 hydroxyphenyl, 2 pentadecyl-d-hydroxyphenyl, p aminophenyl, p nbutylaminophenyl, p-dimethylaminophenyl, pcyclohexylaminophenyl, p methylethylaminophenyl and p-diethylaminophenyl.

Those substituents R1, R3 and R4 which are chosen primarily to impart superior compatibility properties to the compounds of our invention include alkyl, aryl, aralkyl, and alkaryl groups and substituted derivatives thereof. For example we have obtained good miscibility characteristics and maintained the high antioxidant efiectiveness of the compounds of our invention by various combinations of hydrogen, o-chlorophenyl, phenyl, naphthyl, tolyl, methyl, ethyl, npropyl, isopropyl, n-butyl, amyl, pentadecyl, noctadecyl, cyclohexyl, benzyl, p-ethoxyphenyl, pmethoxyphenyl, and fi-hydroxyethyl groups on the N-' and N'-nitrogen atoms or on the substituted phenyl radical characteristic of the compounds of our invention.

While we do not intend that our invention be limited by the choice of the groups R1, R3 and R4, in the preferred embodiments of our invention these groups do not contain excessive amounts of certain atoms and radicals capable of oflsetting the activating influence of the substituted phenyl radicals. .For of halogen atoms or nitro groups are not preferred, although minor amounts can be tolerated.

The compounds of our invention may be further defined by reference to the following methods of preparation, which, while not restricting the scope of the variations possible in different embodiments of our invention, are representative of methods employed by us in preparing the specific materials described herein.

Method I Unsymmetrical disubstituted ureas and thioureas of our invention have been prepared by reaction between substituted phenyl or alkyl isocyanates or isothiocyanates, and substituted anilines or alkylamines, one combination of which is represented by the equation example, excessive amounts A A cum-CD cs, @NiC-NH-CD phenyl)thiourea, N (n octadecyl) N(p-hydroxyphenyhurea, N (p-tolyl) -N'-(p-hydroxyphenyl) urea, N phenyl N- (p-hydroxyphenyl) urea, N phenyl N'-(2-pentadecyl-4-hydroxyphenyD-urea, N phenyl N-(3-methyl-4-hydroxyphenyhurea, N,N' diphenyl N (p hydroxyphenyDurea, N phenyl N'-(p-dimethylaminophenyDurea, N phenyl-N-(n-butyl)-N'- (p hydroxyphenyl) urea, N (p-ethoxyphenyD- N (p-hydroxyphenyl) urea, N- (n-octadecyl) -N- (p-dimethylaminophenyl) urea, N-phenyl-N'- (ohydroxyphenyl) urea, N-phenyl-N' (pdimethylaminophenyl) thiourea, N phenyl N (m hydroxyphenyDurea, N (B naphthyl) -N'(p-hydroxyphenyDurea, N (p-chlorophenyl)-N'-(phydroxyphenyl) urea, and N-octadecyl-N'-phenyl-N- (p-hydroxyphenyl) urea.

Method II Symmetrical thioureas containing two of the characteristic activating groups of the compounds of our invention have been prepared by heating carbon disulfide and substituted anilines in the presence of elemental sulfur according to the equation R4 R4 By this method we have prepared the following examples of the compounds of our invention: N,N -bis(p-hydroxyphenyl) thiourea and N,N- bis(p-dimethylaminophenyl) thiourea.

Method III Certain symmetrical disubstituted ureas of our invention are prepared by warming an aqueous solution of the appropriate aniline hydrochloride with; urea. This method is illustrated by the manufacture of N,N'bis(p-hydroxyphenyl)urea.

Method IV where R is an alkyl group. By this method we have prepared N- (p-hydroxyphenyl) -N'- (p-nbutylaminophenyhurea, and N (p hydroxyphenyl) N'- (p-isobutylaminophenyl) urea.

Method V Symmetrical disubstituted ureas of our invention can be prepared by treating an aniline with phosgene, according to the equation As an example of this method we have prepared N,N-bis (p-hydroxyphenyl) urea thereby.

The compounds of our invention have wide utility in protecting elastomeric substances. Thus, we can increase the useful life of the natural rubbers, such as para or Hevea rubber, and India or Ficus rubber. Likewise synthetic elastomers, such as the butadiene or butadienestyrene polymers, and the polyisobutylenes, can be protected against oxygen or ozone deterioration by our compounds. Furthermore, our antioxidant materials can be incorporated at any of various stages of the manufacturing operations, such as in the synthetic monomers, the polymeric or natural latexes, or during the coagulation, compounding, milling, or fabricating operations.

To illustrate the utility of the compounds of our invention in protecting such substances we selected a natural rubber compounded into a typical tire-tread formula. One requisite of such stocks is that the desirable properties incorporated therein by careful selection of the compounding ingredients and cure time shall be maintained during extended periods of storage or use in the presence of oxygen. Comparison of various rubber stocks is best carried out on stocks initially having the same state of cure. The most reliable means for determining the state of cure is by the T-50 test, AS'IM designation: D599-40T, described in the ASTM Standards for 1946, Part III-B. This test measures the temperature at which a test piece recovers its elasticity when it is stretched at room temperature, frozen at a sufficiently low temperature to cause it to lose its elastic properties, and then gradually warmed. In practice the temperature noted is that at which the sample recovers to 50 percent of the original elongation and is, therefore, referred to as the T-50 value. In the examples that follow, stocks for testing and comparison were cured for a time sufiicient to have a T-50 value of 1 C.,

so that a valid comparison of the properties could be made. The accelerated aging was conducted by the procedure of ASTM designation: D572-42, described in the ASTM Standards for 1946, Part III-B, for a period of 96 hours at a temperature of 70 0., with an initial oxygen pressure in the test bomb of 300 pounds per square inch gauge on specimens having the following composition:

Parts by weight To demonstrate the protection aiforded to the rubber by the compounds of our invention, the tensile strength and the ultimate elongation of stocks prepared with the addition of the anti- 6 oxidants of our invention were determined bet-ore and after aging and were compared with the same properties determined on an identical rub. ber stock not protected bythe compounds o our invention but having the same state of cure, Both of these properties were determined by means of the test procedure of ASTM designa: tion: 13412-41, fully described in AS'I'M Standards for 1946, Part III-B. The tensile strength is the tension load per unit cross-sectional area required to break a test specimen, hile the ul-. timate elongation is the elongation at the moment of rupture of a test specimen. A decrease in the values for either of these properties upon aging represents a decrease in the usefulness of the article fabricated therefrom. Thus, the degree to which these properties are retained is a direct measure of the utility of the protective substance,

TABLE EFFECT ON AGING PROPERTIES OF RUBBER By referring to the table it is at once apparent that all samples containing representative members of the compounds of our invention (Nos. 1, 2, 3, 4, and 5) showed a remarkable increase in the retention of the original tensile strength and ultimate elongation over the control which contained no protective additive (No. 6). Comparing No. 8 with Nos. 1 through 5 clearly shows the activating influence of the above-described grouping essential to the preferred embodiment of our invention. Thus, in the absence of the hydroxyl or substituted amino groupon the phenyl-urea or thiourea, as in N,N'-diphenylthiourea, not only is there a lack of protective action, but the unsubstituted phenyl-thiourea acts as a pro-oxidant, that is the rubber has lost a greater proportion of its desirable properties upon aging when this compound is incorporated therein, than in its absence. Similarly, the o-phenylenethiourea exhibits a similar pro-oxidant effect, despite the fact that this compound has been claimed as an effective antioxidant.

The quantities of the compounds of our invention incorporated in the materials to be stabilized are not critical and depend largely upon the type of elastomer or formulation being stabilized and the conditions under which the exposure to oxygen occurs. For the majority of applications the compounds .of our invention are preferably employed in amount between the limits of approximately 0.1 and 2.0 parts per parts of material to be stabilized, although somewhat larger amounts of the stabilizers of our invention can be tolerated and in some instances are preferred. Thus, our compounds can be satisfactorily employed in a wide range of concentrations, and we do not intend that our invention be restricted to the specific quantities mentioned herein.

We have disclosed a number of preferred embodiments of our invention and illustrated several means whereby protection can be afforded to elastomeric materials sensitive to attack by oxygen. Our invention is not intended to be limited to the specific embodiments of our invention herein or to the means described herein for obtaining the advantages possible in employing our compounds, as other methods of practicing our invention will be apparent to those skilled in the art,

-We claim:

1 .*An elastomeric formulation containing a rubber-like olefin-containing hydrocarbon polymeric elastomer normally susceptible to atmospheric deterioration and containing as an antioxidant ingredient, in quantity sufficient to inhibit such deterioration, substituted urea wherein at least one of the nitrogen atoms is substituted with a radical selected from the group consisting of hydroxyphenyl, aminophenyl, andalkylaminophenyl, and the other nitrogen atom is substituted with an alkyl radical.

2. The formulation of claim 1 in which the antioxidant ingredient is a substituted urea wherein at least one of the nitrogen atoms is substituted with an hydroxy phenyl radical and the other nitrogen atom is substituted with an alkyl radical.

3. The formulation of claim 1 in whichthe antioxidant ingredient is a substituted urea wherein at least one of the nitrogen atoms is substituted urea wherein at least one of the nitrogen atoms is substituted with an aminophenyl radical and the other nitrogen atom is substituted with an alkyl radical.

4. The formulation of claim 1 is which the antioxidant ingredient is a substituted urea wherein at least one of the nitrogen atoms is substituted with an alkyl aminophenyl radical and the other nitrogen atom is substituted with an alkyl radical.

EUGENE F. HILL. DAVID 0. DE FREE.

No references cited. 

1. AN ELASTOMERIC FORMULATION CONTAINING A RUBBER-LIKE OLEFIN-CONTAINING HYDROCARBON POLYMERIC ELASTOMER NORMALLY SUSCEPTIBLE TO ATMOSPHERIC DETERIORATION AND CONTAINING AS AN ANTIOXIDANT INGREDIENT, IN QUANTITY SUFFICIENT TO INHIBIT SUCH DETERIORATION, SUBSTITUTED UREA WHEREIN AT LEAST ONE OF THE NITROGEN ATOMS IS SUBSTITUTED WITH A RADICAL SELECTED FROM THE GROUP CONSISTING OF HYDROXYPHENYL, AMINOPHENYL, AND ALKYLAMINOPHENYL, AND THE OTHER NITROGEN ATOM IS SUBSTITUTED WITH AN ALKYL RADICAL. 